Apomorphine has been used to treat Parkinsonian patients. See, for example, Deffond et al., J. Neurology, Neurosurgery, and Psychiatry 56:101-103 (1993) and Durif et al., Clinical Neuropharmacology 16(2):157-166 (1993). Additionally, apomorphine has been considered for the treatment of alcoholism, schizophrenia, dystonia musculorum deformans, hallucinations, migraine headaches, hiccups, Huntington's chorea, tardative dyskinesia, and more recently male erectile dysfunction.
Administration of large doses of apomorphine to mammals such as humans, dogs and the like usually results in nausea and vomiting, and is believed to be due to the action of apomorphine on the chemoreceptor trigger zone (CTZ) of the medulla oblongata, a structure of the mammalian central nervous system. It is also believed that additional chemoreceptors triggering emesis are present in the gastrointestinal tract as well.
Impotence or male erectile dysfunction is defined as the inability to achieve and sustain an erection sufficient for intercourse. Impotence in any given case can result from psychological disturbances (psychogenic), from physiological abnormalities in general (organic), from neurological disturbances (neurogenic), hormonal deficiencies (endocrine) or from a combination of the foregoing.
These descriptions are not exact, however. There is currently no standardized method of diagnosis or treatment. As used herein, psychogenic impotence is defined as functional impotence with no apparent overwhelming organic basis. It may be characterized by an ability to have an erection in response to some stimuli (e.g., masturbation, spontaneous nocturnal, spontaneous early morning, video erotica, etc.) but not others (e.g., partner or spousal attention).
The effect of apomorphine on penile tumescence in male patients afflicted with psychogenic impotence has also been studied. These studies show that while apomorphine can indeed induce an erection in a psychogenic male patient, the apomorphine dose required to achieve a significant erectile response is usually accompanied by nausea or other serious undesirable side effects, including hypertension, flushing and diaphoresis (sweating). The specific mechanisms by which apomorphine acts to produce an erectile response in a human patient are not yet completely understood, however.
Moreover, apomorphine has been shown to have very poor oral bioavailability. See, for example, Baldessarini et al., in Gessa et al., eds., Apomorphine and Other Dopaminomimetics, Basic Pharmacology, Vol. 1, Raven Press, N.Y. (1981), pp. 219-228. Thus the search is continuing for an effective treatment of psychogenic impotence in male patients as well as for diagnostic methods that can identify such patients.
It has now been found that certain delivery systems for apomorphine can provide a practical therapeutic and/or diagnostic "window" while reducing the likelihood of undesirable side effects.
Acute and subacute testing of apomorphine HCl has been reported in studies with daily doses ranging to over 300 milligrams per kilogram (mg/kg) in lower vertebrates (amphibian and birds), and to 10 mg/kg in higher mammals (primates). In mammals, it appears doses of apomorphine HCl are tolerated up to about 13 mg/kg in a single bolus subcutaneous injection. Doses at or above this amount have been reported lethal in mouse, although, the LD50 is considerably higher (&gt;50 mg/kg) in this species. Continuous infusion of apomorphine has been tolerated and reported to doses of 420 .mu.g/kg/hr for 14 days. Larger doses (1,500 .mu.g/kg/hr were found to be minimally lethal over the course of the 14 day study). In primates, multiple doses of apomorphine HCl have been administered for up to four days at 100-400 .mu.g/kg without major adverse effects.
However, in 1995, The Pharmacology of Sexual Function and Dysfunction (J. Bancroft, editor), in an article at pp. 225-229 entitled "Dopamine agonists and their effect on the human penile erectile response" by R. T. Segraves, M.D., summarized evidence concerning the use of dopamine agonists especially apomorphine to induce erectile responses in human males. The article concludes that "[c]learly, apomorphine has too many side effects to have therapeutic usefulness."
Notwithstanding the Segraves article, apomorphine dosage forms have been found to be effective in treating Parkinson's disease as well as in male patients suffering from psychogenic erectile dysfunction for the induction and maintenance of an erection sufficient for intercourse (i.e., vaginal penetration). While at relatively lower dosages apomorphine can be administered without nausea or other undesirable side effects, such side effects do manifest themselves as the dosages of apomorphine are increased.
When the plasma concentration of apomorphine is maintained at no more than about 5.5 nanograms per milliliter (ng/ml), the incidence of adverse side effects is minimal. Such monitoring, of course, requires either an invasive procedure, such as blood analysis or urinalysis, to determine proper dosing requirements.
The present method provides for the amelioration of adverse effects due to apomorphine use without the invasiveness of previous methods.